Over the past several decades, many advances have been made in improving the efficiency of weighing of batches of products for filling packages, such as pillow-type packages on a form, fill and seal packaging machine. A considerable improvement has been made in the technology of computerized combination weighing, that is where multiple product batches or charges are sampled and combined to make one product charge. These advances have not only provided an increase in speed of the overall packaging system, but have proven very successful in reducing product give away. A leading approach in computerized weighing is set forth in the computer circuit described and claimed in U.S. Pat. No. 4,418,771 entitled "Method and Apparatus for Combination Weighing" and 4,538,692 entitled "Method and Apparatus for Combination Weighing With Multiple Storage Cups for Each Scale Hopper", owned by the present assignee.
While there have been several attempts to improve the operation of the control circuit of the computerized weighing machines, little attention has been given to improving the handling of the product in the hoppers that form and weigh the batches. In terms of efficiency, the best arrangement has remained substantially unchanged since the time of the original machines and methods set forth in the '771 and the '692 patents. Specifically, in the past, the typical arrangement includes a scale hopper positioned to receive the stream of flowing product directly from a vibrating feed conveyor, and then once weight is made the batch is transferred to one or more holding hoppers or cups. In order to make certain that late, in flight product is not introduced into the scale hopper, a lip gate is provided at the end of the vibrating feed conveyor in these prior art systems. Some effort has been made to introduce a third hopper into the system, but with limited success. One such attempt is characterized by a pool hopper positioned above the weighing hopper to receive the flow of product from the feed conveyor. Since the weight of the product in the pool hopper is unknown, this hopper cannot participate in any manner in the combination weighing and selection process.
Furthermore, improving the efficiency of operation of the hopper itself and simplifying its structure has not attracted significant attention in the field. An example of this is that lip gates are still used in most arrangements to accurately cut-off flow into the batch forming/weighing hopper. Other inventors have resorted to using the pool hopper above the forming/weighing hopper in an attempt to alleviate the late, in flight product problem. Also, some inventors have been led to the use of a separate shutter positioned between the lip of the feed conveyor and the first in line hopper to catch the late product in flight; however, such an arrangement requires substantial additional mechanical components and operating mechanism which makes it an expensive alternative. Similarly, the operating mechanism for opening and closing of the gates of the hoppers have continued to be complicated and characterized by a large number of component parts, primarily linkages and springs. Still, no truly efficient approach to rapidly open and close the gates for efficient transfer of the formed batches of products has heretofore been found. Furthermore, these prior art operating mechanisms are not only more expensive to manufacture, but make clean up of the weighing machine much more difficult.
Besides the improvements in the control circuitry, some improvements have been made in other sections of the packaging machines, such as set forth in U.S. Provisional Pat. Application Ser. No. 60/000,750, filed Jun. 30, 1995 and entitled "Packaging System With Improved Transitional Product Flow and Adaptive Control". Furthermore, substantial advances in continuous feed of the packaging film, the actual forming of the packages has likewise reached a very advanced state, such as provided in U.S. patent applications Ser. Nos. 08/212,548 and 08/350,877 and entitled "Continuous Vertical Form-Fill-Seal Packaging Machine With Constant Motion Carriage" and "Continuous Vertical Form-Fill-Seal Packaging Machine With Synchronized Product Clamp", also owned by the assignee of the present invention. Such a scenario provides additional impetus to improvement in the efficiency and overall speed of the weighing system in order to reach the next level of operating efficiency and technology in the form, fill and seal packaging industry.
Thus, an important aspect of the present invention is to provide a multiple in-series hopper system and related method that improves the product batch or charge weighing and transfer of successive batches for maximizing the speed and efficiency of the packaging system.